The present invention pertains to method and apparatus for performing visual field tests. In particular, the present invention relates to method and apparatus for performing video-based visual field tests and stimuli-contrast visual field tests.
As is well known, methods of testing human visual functions include determinations of: (a) contrast sensitivity; (b) flicker frequency sensitivity; (c), visual resolution acuity; and (d) color sensitivity. Apparatus that can carry out such tests are referred to as automatic perimeters or visual field testers, and such apparatus have been known in the art for many years.
A Standard Automatic Perimeter (SAP) that is known in the art and is used to perform a contrast sensitivity test includes a hemispherical projection surface and a stimulus optical projection system. In a typical such SAP, the hemispherical projection surface is uniformly illuminated (using a white light source) to provide a constant and uniform background illumination, and the stimulus optical projection system projects a circular spot on the hemispherical projection surface to provide a stimulus to the human vision. The radius of the hemispherical projection surface is about 30 cm to enable the subject to see the stimulus comfortably (i.e., without straining the subject""s test eye), and the position and brightness of the stimulus are specified by a computer implemented algorithm. In use, a subject is asked to respond to the stimulus by pressing, for example, a mouse button, and the contrast sensitivity of the subject""s visual field is mapped by changing the brightness and position of the stimulus on the constant, uniform background illumination.
U.S. Pat. No. 5,323,194 discloses an SAP having reduced size in a peripheral field region. This reduced size is produced by changing the shape of the projection surface from a hemisphere to a hemisphere. However, a central field region still uses the same distance from the subject as is used in the hemispherical SAP.
U.S. Pat. No. 5,046,835 discloses that the size of an SAP can be reduced by using a cupola-less optical system. In such a cupola-less optical system, the stimulus is presented to the subject by illuminating a diaphragm with light output from an LED, a halogen lamp, or a laser light source while the background is illuminated with light output from a diffused light source. The stimulus and background are combined, and projected onto the subject""s retina to perform the visual field test.
Despite the above-described improvements, presently available SAPs can only perform static contrast sensitivity tests. This is because: (a) the speed of the optical projection system is limited; (b) mechanical movement of a diaphragm of the SAP is too slow to generate a video-based visual test pattern; and (c) it is impossible to generate a video-based visual test pattern since background illumination is provided by a diffused light source.
A flicker frequency sensitivity visual field test requires a video system to generate a high frequency test pattern. One commercially available flicker frequency sensitivity visual field tester is called a Frequency Doubling Technology (xe2x80x9cFDTxe2x80x9d) Visual Field Instrument. The FDT tester includes a cathode ray tube (xe2x80x9cCRTxe2x80x9d) and viewing optics to display a high frequency test pattern with a forty (40) degree field of view. However, due to brightness limitations of current CRTs, and limitations in the field of view of the viewing optics, the FDT tester cannot perform a contrast sensitivity test like that performed by the SAP.
In light of the above-described limitations, there is a need in the art for an apparatus that is relatively small in physical size, and is capable of performing: (a) a contrast sensitivity test; (b) a flicker frequency sensitivity test; and (c) other visual field tests that require a video test pattern (for example, a visual resolution acuity test).
Embodiments of the present invention advantageously satisfy the above-identified need in the art, and provide an apparatus that is relatively small in physical size. and is capable of performing: (a) a contrast sensitivity test; (b) a flicker frequency sensitivity test; and (c) other visual field tests that require a video test pattern (for example, a visual resolution acuity test).
Specifically, a first embodiment of the present invention is a visual field tester that comprises: (a) a high intensity light source; (b) an optical fiber; (c) scanning optics, wherein light output from the light source is directed by the optical fiber to impinge upon the scanning optics, and the scanning optics directs the light to form a stimulus at various field positions; and (d) a video display system to output one or more light patterns.
A second embodiment of the present invention is a visual field tester that comprises: (a) a video display system to output one or more types of light patterns; (b) a background illumination display system; and (c) viewing optics to magnify the field of view of the video display system and the background illumination display system.
A third embodiment of the present invention is a visual field tester that comprises: (a) a video display system to output one or more types of light patterns; and (b) a background illumination display system that outputs variable intensity light, wherein the video display system comprises: (i) a variable intensity, high brightness light source and (ii) a light modulator display disposed to transmit light output from the source. In accordance with a further variation of this embodiment, the visual field tester further comprises a controller to control the variable intensity, high brightness light source and the background illumination display system.